1. Field of Invention
The present invention relates to a method for correcting projected image distortion that occurs when an image is projected by a projector obliquely on a projection surface.
2. Description of Related Art
In a projector, light emitted from an illumination optical system is modulated by a spatial light modulator, such as a liquid crystal light valve (liquid crystal panel) according to an image signal. The modulated light is projected on a projection surface, and thus an image is displayed. Examples of spatial light modulators may include, but not be limited to the crystal light valve. For example, a projector may employ Digital Micromirror Device™ (a trademark of Texas Instruments Incorporated) or devices using other technologies.
When an image is projected on a projection surface with the central axis of light for forming an image (image light) emitted from a projector not corresponding to the normal of the projection surface, the image displayed on the projection surface will be distorted. Even if the projector is to project a rectangular image on the projection surface, the image displayed on the projection surface may be distorted into a shape not rectangular but rather quadrangular. The distortion of the projected image can be corrected by adjusting the shape of an image formed by image light emitted from a liquid crystal light valve, in other words, by adjusting the shape of the image formed in the area of optical modulation (imaging area) of the liquid crystal light valve.
FIG. 11 shows an exemplary method for correcting the distortion of the projected image. FIG. 11A-1 shows a rectangular image IMa “original image IMa”) that is formed in a rectangular imaging area of the liquid crystal light valve in the case where no distortion correction is applied. In this case, a quadrangular image IMaS that has been distorted into a shape not rectangular is displayed on the projection surface as shown in FIG. 11A-2. Here, the image shown in FIG. 11A-2 is projected obliquely on the projection surface from the lower right to the normal of the projection surface.
FIG. 11B-1 shows a corrected image IMc that is formed in the imaging area of the liquid crystal light valve in the case where the distortion of the projected image shown in FIG. 11A-2 is corrected. The corrected image IMc consists of a distortion correction image IMc-a and a background image IMc-b. The distortion correction image IMc-a is an inverted image of the image shown in FIG. 11A-2, and is formed by transforming the original image IMa. The background image IMc-b is composed of black pixels. As the corrected image IMc is formed in the imaging area of the liquid crystal light valve, only the distortion correction image IMc-a in the corrected image IMc is projected. Consequently, a rectangular image IMcS (IMc-aS) shown in FIG. 11B-2 is displayed on the projection surface.
An exemplary method for transforming the original image IMa so as to form the distortion correction image IMc-a is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2002-6391 and Japanese Unexamined Patent Application Publication No. 2003-46907.